A conventionally known diaphragm valve includes: a body having a fluid inflow channel, a fluid outflow channel, and a depression opening upward; a seat demountably disposed on a circumferential edge of the fluid inflow channel of the body; a seat holder demountably disposed on the body to hold the seat; a diaphragm that is pressed against and separated from the seat to open and close the fluid channel; and vertically moving means for vertically moving a diaphragm presser that presses a central portion of the diaphragm (Patent Literature 1, etc.).
The seat holder includes a plurality of through holes that communicate with the fluid outflow channel. In an open state in which the diaphragm is separated from the seat, a fluid that has flown into the fluid inflow channel enters a space created between the diaphragm and the seat and then flows into the fluid outflow channel through the through holes communicating with the fluid outflow channel.